Broad band frequency discriminator



June 26, 1951 H. CHIREIX 2,558,604

BROAD BAND FREQUENCY DISCRIMINATOR Filed March 25, 1948 By v I: I

AGENTS Patented June 26, 1951 V v N I TED I 1:15 PATEN FF ICE BROAD BAND DISCRIMINATQR Henri Chireix, Paris, France; S ociete aes ies lia gf ia aa r or t 9 =f Kiifllication March 25, 1948, Serial N 0. 16,966

M n v,

I Et ance April-15 1947 la c1."-52'5t "2"7) The present invention relates to frequency disinstantaneous frequency deviation. As none of theseconditionsquexcept theone relating to.- the value of a l,

24 5 B0. can in eflect be satisfied with sufficient precision, such a discriminator can-offer acceptable F ZE gi 2 fif ijffi results only when more or less close compenw? 1 c .v sations are made. mven In the present invention, the various defects Fig; 4 shows a forin of filter for use in conjunction with the apparatus of Fig. 3; and

Fig. 5 is a generaLdiagram-showing how the apparatus of Fig. 3 may be incorporated into are eliminated by employing, instead of two coupled-;;cir,cuits as inrFigeiI; thenbridge :of Fig. 3. consistingaoitwo identical inductancesax and two; identical capacities n6, "forming, 12a unit resonating with the pulsation C5351"; r:

- 132-. V Said bridge is closed on its" characteristic impedanbe 1 a 1 n... l, w lt. e inDQ 99 91?l ith-ihs taq ef e Wel Said discriminator is supplied with constant current i, the current -2' being furnished by an amplitude limiter of whichonly the anodic cir- R: l cuit l is shown. I T

It comprises essentially two coupled circuits, constituted by a pure resistance, the two detecf primary-and a which-thewlatter tors being connectedto terminals Bi and C, sym tunemcto-the-mld4mquemy 30496 "d metricalswithx, respectito the niid-point LA and nated and.deliverseto two-detectors d-loacled by including between partt f the resist; equal-{reS1Stan-CeS?T-. '-The -dlsorlml-nated a-nd-fi ance upplied constant tented potentlalflis collected at- NM=- current i. The:rcs1ilt',-'is thatwat all frequencies .mThe. well-knownmodeofoperation of this'art rangement isshown-in- EigV-Qt -Let- 0A hethe l m potential at-vtheterminalsof the winding "of the primarylcircuit BC-the potential -at-the termi ofathe secondary circuit.gone of;-the detectorsaisi-subjected with respect tothe middle of the secondary winding to the resultant po'- tential 04+ 13 :0 i3, the'other'tothe potenti and that sin 0 of Fig. 2 is given by the relationa s-5., ship on zig'=OQ,"so that the potentiarcouec din 4 M .p slporfl n t I BII CI.- .-I ar icula P itis a? 11 tu i Qti a e nd yae m it with BC' -being'in quadrature =witn'0ir:" =2=n+&= & -.This vclassical circuit;involves numerous dee: fectsrwhen an attempt is made to applyi 110 where an, is the mean pulsation of the frequency perfectly li e r tq iq m d modulated wave, up the resonance pulsation, Aw lowebthanfio 430 d b l 'h and 1' the z instantaneous frequency deviation, .-:;.-and the .discriminationofa deeply -modulated-wave here he; (relative deviations higher than 5 or l0'-%).---- t H r K w! Correct operation assumes indeed: that 0A 1 and AB, AC remain constant in modulus when For a smusoldal f i the frequency ,varies in the Vfrequencya band C05 M Cir frequency.

thus be m 1--AA 61. Minus:

tdbe covered, .I h tfitfielaliia I in which (2 is the pulsation of the modulating seen that if 'HHT! H a TK is greater than 5 for example, or smaller than and that sin a is strictly proportionali-to'the 9 most of the conditions satisfied at all frequencies, from zero frequency up to a higher limit, which is attained when each induction element A behaves no longer as an inductance but as a parallel-connected inductance-capacity unit, and each capacity Y no longer as a pure capacity, but as a seriesconnected capacity-inductance unit. A more can be developed as a function of thus determining the rate of harmonics based on-the fundamental term for a' modulation of sinusoidal frequency at the input. This is summarized in the following table:

funda- 2nd har- 3rd liar- 4th har- K? mental moruc momc momc Degrees 3 Am 3 w 3 1 Am 2 3 Au 3 2; 5(a) is a) 64 a) an 4 m i ne 2 a :2 ay 3 49 on '28 an i 21 on 3M Am 3 Am 3 2 a r a) 2 (a) The above table brings out the importance of regulating the bridge on the pulsation corresponding to and to 0o=30 (Fig. 2),

r being the angle of AB with AO-in' the absence of frequency modulation.

It will thus be seen that under these conditions the most important harmonic is the third and that its relative value is f criminator regulated as previously set forth,

the high frequency harmonics of the second and third order will correspond respectively to and K =3; the table thus gives the values of the low frequency harmonics generated in this manner and based on the corresponding fundamental. It will be seen that it is possible thus to produce a very aperiodic discriminator since it is possible to discriminate, besides the normal frequency modulated wave, harmonic frequency modulations of the same relative width of band.

It may be desirable to have the circuits of the discriminator preceded by a filter of har-' monies, which of course must not change appreciably the transmitted amplitude. This filter may be constructed in accordance with the installation of Fig. 4 comprising the inductances L1, L2 and the capacities C1, C2 and where Z0 is the impedance between 0 and D of Fig. 3; this impedance is also R. Otherwise the circuit of Fig. 4 has the dimensions to satisfy the relations that is to say that it is tuned to the mean frequency of the frequency modulated wave, and L1=0.5C2R Such a' circuit gives at the terminals of Zn a very fiat response curve as a function of the frequency. Particularly we can make Fig. 5 shows by way of a non-limiting example a discriminator according to the invention. In this figure we find again, with the same reference characters, the elements presented before in the preceding figures: l designates the anodic circuit of the limiter; the unit LiCiLzCz constitutes the cell of the harmonics filter; A and 'y are the inductances and capacities of the bridge, the diagonal of which contains the resistance R, d and r the detectors and the load resistances, M and N the points to which the detected potentials are applied.

What I claim is:

A frequency discriminator which comprises in combination a frequency responsive network of the bridge-type wherein two opposite arms in-. clude, substantially identical capacitances and two other opposite arms include substantially identical inductances, means for applying frequency modulated currents of a constant intensity to one diagonal of the bridge, means for grounding one terminal of the same diagonal, a resistor connected in the other diagonal of said bridge and having a resistance substantially equal to to one another the two electrified voltages thus obtained and means for picking up the difference of said voltages, said difference being substantially proportional to the deviation of the instantaneous frequency from the mean frequency of 5 said currents.

HENRI CHIREIX.

REFERENCES CITED The following references are of record in the 10 file of this patent:

Number 6 UNITED STATES PATENTS Name Date Logan Mar. 21, 1939 Ballard Mar. 12, 1940 Hansell May 27, 1941 Schonfeld Dec. 2, 1941 Rankin Oct. 26, 1943 Sprague June 12, 1945 

